Ultrathin diamond (diamane)-like films or nanosheets have recently been experimentally obtained through chemically induced phase transition (e.g., fluorination) of bilayer graphene films or graphite flakes. To fully exploit the properties of diamane, further advances in the synthesis methods for its large-scale production are required. Herein, we report a new route for the efficient and high-yield production of fluorinated diamane (F-diamane)-like nanosheets. This is achieved by direct fluorination of expandable graphite or thermally expanded graphite with molecular fluorine to form stage-2 graphite fluoride (C2F)n made of stacked layers of F-diamane. Subsequently, mild sonication is implemented to exfoliate the layers into F-diamane-like nanosheets of hundreds of nanometers to a few micrometers in lateral size, with a thickness of mostly < 10 nm.